SB
818
C578
ENT

Issued July 27, 1912,

U.S. DEPARTMENT*OF AGRICULTURE,
BUREAU OF ENTOMOLOGY—CIRCULAR No. 158.
- L. O. HOWARD, Entomologist and Chief of Bureau.

THE CLOVER MITE.

BY

7

FM. WEBSTER,

In Charge of Cereal and Forage Insect Investigations.

42056° —Cir. 158—12

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1912

A OG,

BUREAU OF ENTOMOLOGY.

L. O. Howarp, Entomologist and Chief of Bureau.
C. L. Maruatt, Entomologist and Acting Chief in Absence of Chief.
R. S. Cuirton, Executive Assistant.
W. F. Tastet, Chief Clerk.

F. H. CuirrenbDen, in charge of truck crop and stored product insect investigations.
A. D. Hopkins, in charge of forest insect investigations.

W. D. Hunter, in charge of southern field crop insect investigations.

¥. M. WesstTeER, in charge of cereal and forage insect investigations.

A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.

E. F. Puriies, in charge of bee culture.

D. M. Rocers, in charge of preventing spread of moths, field work.

Roiia P. Currin, in charge of editorial work.

MaBeL CoLcorD, in charge of library.

CEREAL AND FORAGE INSECT INVESTIGATIONS.
F. M. WEBSTER, in charge.

Gro. I. Reeves, W. J. Puitiies, C. N. AINsiiz, EH. O. G. Ketty, T. D URBAHNS,
Harry S. SmitH, Gro. G. AINSLIE, J. A. HySLtor, W. R. WALTON, J. T. MONELL,
J. J. Davis, T. H. Parks, R. A. Vickery, V. L. WILDERMUTH, HE. G. SMYTH,
HERBERT T. OSBORN, PHILIP LUGINBILL, C. W. CREEL, E. J. VOSLER, R. N. WIL-
soN, VERNON KING, GeorcE R. SmirH, IrvinG CrAwrorpD, entomological as-
sistants.

Nettie 8S. Kioprer, ELLEN DASHIELL, preparators.

Mieram WELLES REEVES, collaborator.

II

CIRCULAR No. 158.

Issued July 27, 1912.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

THE CLOVER MITE.

(Bryobia pratensis Garman. )

By F. M. WEBSTER,

In Charge of Cereal and Forage Insect Investigations.

INTRODUCTION.

The minute organism known as the clover mite (fig. 1) is not a
true insect, but belongs, with the spiders, to a very extensive group

the adults of which possess
eight legs, whereas true in-
sects have only six legs.
There are a great many
species of these mites and
they differ widely among
themselves in habits. Some
make galls on the leaves of
trees and shrubs; some, like
the one which commonly at-
tacks the currant, are known
as blister mites, as they
cause blisters on leaves;
others are parasitic on man,
as the itch mite; while still
others, like the Trombidium,
are parasitic on_ insects.
Another, Pediculoides ven-
iricosus Newp., 1s parasitic
on insects but also attacks
man. The one here treated
lives on the surface of
leaves of trees and plants,
but does not cause galls or
blisters. It isa near relative
of the notorious red spider.

hay :

Fic. 1.—The clover mite (Bryobia pratensis).
Enlarged; natural size shown by line at right.
(From Insect Life.)

The clover mite, also known as the brown mite, is of a twofold
interest. It attacks the leaves of clover, grasses, and fruit and other

1

2 THE CLOVER MITE,

trees, feeding upon and often destroying them; besides, during winter
and spring it frequently swarms in dwellings, often crawling about
in myriads over windows, furniture, pictures, curtains, ete.

The species was first described in 1885,’ but it was observed in great
abundance about Washington, D. C., by Mr. Theodore Pergande, of
the Bureau of Entomology, as early as 1878. While described as a
clover-infesting species, having been found infesting clover leaves by
both Mr. Pergande and Prof. H. Garman, yet taken as a whole
throughout its known area of distribution it is probably of more im-
portance to the fruit grower than it is to the farmer. While east of
the semiarid region it is found largely on clover and bluegrass, it
is at present largely an orchard pest west of about longitude 100°.

@=BAYORKlN PARATENSS

Fic. 2.—Map showing the distribution of the clover mite (Bryobia pratensis) in the
United States in 1911. (Original.)

DISTRIBUTION.

With the possible exception of Georgia the pest seems to occur
generally over the whole country, except perhaps in the Gulf States
and the Dakotas, though just why it should not be found even there
can not now be explained. (See map, fig. 2.) Mr. Marlatt? states
that it has been reported from Tennessee, and in the Sierra Nevada
Mountains in California and Rocky Mountains in Montana at ele-
vations of from 7,000 to 8,000 feet, but exact localities are not given.

The mite was described from the leaves of red clover (77rifolium
pratense) from which it derives its last or specific name. Accom-

1 Fourteenth Rept. St. Ent. Ill., pp. 73-74, 1885.
2Cir. 19, Div. Ent., U. S. Dept. Agr., 1897.

THE CLOVER MITE. a

panying the original description’ is the following note by Dr. S. A.
Forbes, State entomologist of Tlinois:

At Normal, early in May, the general occurrence of a large and conspicuous
brownish red mite was noticed upon clover and bluegrass, the former of these
plants, especially, sometimes suffering severely from the pest. The leaves of
the clover turned yellow and their growth was arrested where the mite was
abundant. The effect upon the bluegrass was similar.

As a matter of fact, the bureau records contain reports of the
occurrence of the species over the territory indicated by the map
(fig. 2). These records illustrate its great variety of food plants as
well as the effect of climatic and other natural conditions upon its
habits; they are, however, far too voluminous to include in a publi-
cation of the nature of this circular.

DESCRIPTIONS.

These mites are sufficiently shown in figure 1 to obviate the neces-
sity for a lengthy description. When young they are of a decidedly
red color, but become brown when fully developed, even then being
smaller than the head of a pin. They are very familiar objects
moving about over clover leaves that have a more or less whitish
appearance. The discoloration of the leaves is in part due to the
feeding of the mites, and also to the tiny white web that they leave
behind them as they move about. The eggs are minute, round, red,
and shining.

FOOD PLANTS.

From the foregoing it will be observed that this mite is a general
feeder and may be expected to attack clovers, alfalfa, bluegrass, and
probably other grasses, among them timothy. It may affect oats and
probably other grains including buckwheat. Mr. George P. Weldon
calls attention to the fact that it had not been observed attacking
apricot or quince and appeared less on peach than on most other
fruits in Colorado.?

Judging from what we know of an allied species, Tetranychus
bimaculatus Harvey, the pest is likely to become more abundant
and injurious in the drier sections of the country than where the
atmosphere is more humid. It does not necessarily follow that the
mite will attack the foliage of the tree on which it has deposited eggs.

SEASONAL HISTORY.

Throughout the eastern portion of the country the life cycle and
seasonal history of this species probably do not materially differ
from those of other mites. With the coming ef cold weather in late

1Loc. cit.
2 Bul. 152, Colo. Agr. Coll. Exp. Sta., p. 6, 1909.

4 THE CLOVER MITE.

autumn or early winter the mites apparently cease to deposit eggs,
and thus operations are simply suspended until the coming of warin
weather in spring, when the eggs promptly hatch young mites. This
is clearly shown by the observations of Mr. Pergande.

As will be observed, the presence of mies in dwellings during
fall and spring is of common occurrence. Do they deposit eggs and
do these eggs hatch there? It may be stated that both eggs and mites
were received from Williamsport, Pa., December 11, 1896, and that
the eggs hatched en route. Also, as observed by the writer, the mites
entering a dwelling in Lafayette, Ind., during December, 1889, when
the weather was very mild, were at: first full grown, but young
appeared later in the month. Whether mites seek out dwellings in
which to continue reproduction but die out for lack of food, or
whether they enter them for the purpose of hibernation, is not clear.
Tt is very, clear, however, that they do not go into hibernation in
May, a time when their occurrence in dwellings is of equally common
occurrence. Furthermore, our notes show that complaints of these
mites entering dwellings almost invariably come from the eastern and
cooler sections of the country, the reports from McCook, Nebr., and
Denver, Colo., being the only exceptions in the West. Mr. George P.
Weldon, who studied the species in Colorado,’ states that it winters
there principally in the egg stage and that practically no living
mites can be found abroad after August 1. Hatching begins about
May 1, and there are probably three generations annually in that
region.

REMEDIAL AND PREVENTIVE MEASURES.

Tobacco preparations applied in the form of a liquid spray are
quite effective in destroying the mite, but do not destroy the egg,
and therefore offer only temporary relief. Mr. Weldon found
that flowers of sulphur dusted on foliage during early morning
was more effective in destroying the mites. A liquid spray of 1
pound flowers of sulphur mixed in 4 gallons of weak soapsuds, 1
pound of soap to 100 gallons of water, was very effective and ap-
peared to be lasting in its effects. This last can be easily applied
to lawns and grounds where the mites are at work and also in
fields of clover or alfalfa in case the depredations are confined to
small spots or areas. The eggs can be destroyed on the trunks of
trees by the use of strong kerosene emulsion. The writer has re-
ceived reports of good results in driving the mites away from dwell-
ings by placing oil of pennyroyal in small shallow dishes in the
rooms where the mites occur. This measure does away with the
disagreeable feature of fumigation with fumes of sulphur or dust-
ing with insect powder, and the odor of the oil is not disagreeable
to people using the rooms,

1Loc. cit., p. 3, October, 1909.

THE CLOVER MITE. 5
NATURAL ENEMIES,

The insect enemies of this mite, so far as recorded, are very few.

October 28, 1889, Mr. Pergande reared one of the common clothes
moths (Zineola biselliella Hiibn.) from small caterpillars that he
had observed to feed upon the eggs.

Mr. Weldon’ gives as enemies of the red spider (Zetranychus
Limaculatus Harv.) a minute black lady-beetle, Scymnus punctum
Lec. (fig. 3) and lace-winged flies. As there are many species of

Fic. 3—Scymnus punctum, a lady-beetle enemy of the clover mite: a, Egg; b, larva;
ce, pupa; d, adult. All much enlarged. a, b, c, Redrawn from Weldon; d, original.

the Scymnus and of lace-winged flies, it is not at all unlikely that
some of them prey upon the clover mite.

Approved:
JAMES WILSON,
Secretary of Agriculture.

Wasuineton, D. C., April 18, 1912.

TOG Cling (D> 2.

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